Retrotec DM-2 User Manual
Page 57
Page 57 of 72
©Retrotec Inc. 2012
Any time the gauge sees a positive pressure on Channel A, it automatically subtracts the value on
Channel A from the value on Channel B before calculating flow and other results. The value displayed
for “PrB” is left as the raw measured value and does not have the Channel A value already subtracted.
If using a raw measured value read from “PrB” on a Retrotec gauge, use the following equation to
adjust the Fan Pressure and calculate the flow:
𝐹𝑙𝑜𝑤 𝑇𝑜𝑤𝑎𝑟𝑑 𝑂𝑝𝑒𝑟𝑎𝑡𝑜𝑟 𝐶𝐹𝑀 = ((𝐹𝑃 − 𝑅𝑃) − (𝑅𝑃 × 𝐾1))
𝑁
× (𝐾 + (𝐹𝑃 − 𝑅𝑃) × 𝐾3) × 𝐾4
Where:
FP is the fan pressure from Channel B displayed as “PrB”
RP is the room pressure from Channel A displayed as “PrA”
Case 3: Self Referencing Fan
Self-referencing fans can be identified because they have ports for two pressure measuring tubes on
the fan itself. If a self-referencing fan is the chosen Device then the fan includes a green port as well as
the yellow port and the Fan Pressure signal sent to the gauge is always the correct value and never
needs adjusting. Setting the Device on the gauge to 3000SR or DU200 tells the gauge not to subtract
the room pressure from the “PrB” value before calculating flow.
𝐹𝑙𝑜𝑤 𝑆𝑒𝑙𝑓 𝑅𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒𝑑 𝐶𝐹𝑀 = (𝐹𝑃 − 𝑅𝑃 × 𝐾1)
𝑁
× (𝐾 + 𝐹𝑃 × 𝐾3) × 𝐾4
Where:
FP is the fan pressure from Channel B displayed as “PrB”
RP is the room pressure from Channel A displayed as “PrA”
In all cases:
The absolute value of FP must be greater than the minimum fan pressure, “MF”, shown in Table 11,
and greater than the calculated factor using the K2 value from the table as follows:
|𝐹𝑃| ≥ |𝑅𝑃| × 𝐾2
To determine the flow for a particular fan pressure FP:
Check that the measured value for FP meets the two conditions based on MF and K2. If so, find the N,
K, K1, and K3 values in Table xxx (based on the type of fan and the Range Configuration being used),
enter those values along with the values measured for FP, and RP into the Flow equation stated above
and calculate the result.
Table 11: N and K coefficients for all gauge supported fans.
Range
N
K
K1
K2
K3
K4
MF
DU220
Open
0.5115
30.7774
0.000
0.2
0.0
1.0
10
Mid
0.5415
5.9146
0.000
0.5
0.0
1.0
25
Low
0.6125
1.0056
-0.024
0.5
-0.0002
1.0
25
Retrotec
1000 /
2000 /
Open
0.5214
519.6183
-0.070
0.8
-0.1150
1.0
8.6
A
0.5030
264.9959
-0.075
1.0
0.0
1.0
12
B
0.5000
174.8824
0.000
0.3
0.0
1.0
10